Add the cubed butter and, using your fingers, lightly rub in the butter to the flour mix until is resembles breadcrumbs with some pieces the size of small peas (you can do this in a food processor as well).

Make a well in the middle of the flour mix and add the egg.

Mix the flour into the egg until it just starts to come together.

Add the water and incorporate until the dough just comes together. The dough should be firm enough to form a ball – it might be a little crumbly but press the dough into a disk and wrap it tightly in plastic wrap and refrigerate for 30 minutes minimum.

Meanwhile, make the filling:

Pre-­heat oven to 350 ̊F.

Bake the potatoes for about 35 minutes.

Allow them to cool slightly then slice into even slices, around 1.5cm in width.

Meanwhile, fry the bacon until crispy. When it's cooked, roughly chop into small cubes.

Sautée the onion until it's just starting to turn a deep brown.

Grate the cheese.

To assemble:

Pre-­heat oven to 350 ̊F.

Grease a 10 inch quiche or tart pan.

Remove the dough from the fridge, let sit for a couple of minutes, then roll between parchment or wax paper or onto a lightly floured surface until it is about 13-­14 inches wide.

Remove the pastry from the parchment and press the pastry into the pan (you might need to trim some of the pastry and the parchment around the edges).

Spread the sour cream evenly across the bottom of the pastry case.

Layer about ¾ of the potato slices evenly on the sour cream.

Add about ¾ of the onion, ½ the cheese and ½ of the bacon.

Layer the rest of the potatoes on the filling.

Top with remaining onion, cheese and bacon, layering them evenly.

Fold the uncovered edges of dough up and around the filling, working your way around the pie. You’ll end up with pleated edges that are a little rough and you might need to trim some uneven parts to ensure you don’t end up with a thick area of just crust.

Brush the edges of the pie with a little egg wash.

Bake for 45 minutes or until the pastry is golden and the cheese is melty.